(AP) — More than a year after a blowout at a natural gas facility drove thousands from their Los Angeles homes, state officials showed off repairs and improvements as they work to complete a safety review that could lead to resumed operations.

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A total of 34 wells owned by Southern California Gas Co. have passed a rigorous battery of tests required by the state oil and gas operators since the blowout was capped in February after spewing the largest-known release of methane in the U.S. over nearly four months. The remaining 79 wells are isolated so gas can’t escape and many are undergoing repairs that could eventually return them to service.

“There’s no other facility in the United States that I know of that has gone through the series of tests that Aliso Canyon has gone through,” Ken Harris, the state oil and gas supervisor, said Thursday.

The blowout discovered in October 2015 drove more than 8,000 families from their homes as they complained about headaches, nausea and nosebleeds from the stinky release.

Some residents who live by the facility located in a mountain range next to the suburban San Fernando Valley continue to complain of becoming ill since they returned home and many want to see the facility permanently shut down, arguing it hasn’t been necessary since it ceased operations.

“It has been shown that this facility is not necessary,” said Alexandra Nagy, of Food and Water Watch, a group calling for the shutdown. “The facility has been shut in — no gas in or out of the facility — since January 2016. A year later, this facility hasn’t been used for energy purposes.”

The former oil field that was converted in the 1970s to store gas a mile and a half underground is the largest natural gas facility west of the Mississippi River. The company and state agencies consider it essential for home heating and to power gas-fired electricity plants during energy spikes, though predictions of blackouts last summer never happened.

The blowout happened 895 feet below ground in an oil well more than 60 years old, said Alan Walker, an engineer with the Division of Oil, Gas and Geothermal Resources. It seeped up through the ground and eventually blew a gaping hole in the ground and occasionally released an oily mist.

Signs of the blowout are now gone. The hole is now capped with concrete and bright green grass is sprouting around it due to recent rain. Dumpsters nearby are filled with dirt that may have been contaminated as methane and traces of other hydrocarbons escaped.

SoCalGas has had to install new pipes throughout and make repairs to bring the old wells up to stricter standards required by the state.

State officials said they expect to complete their safety review and hold public meetings before deciding whether SoCalGas can begin storing gas again. They expect those steps should be completed by April.

Each well now has three remote pressure monitors that could more quickly detect or prevent a leak. Before the leak, an employee would typically check the pressure at each well once a day.

Employees in an operations center now scan several large screens that provide real-time information about well pressure and also a series of monitors that measure methane on the edge of the Porter Ranch neighborhood below.

The monitors were installed as part of a $4 million settlement and no-contest plea SoCalGas negotiated with Los Angeles prosecutors for failing to immediately notify the state of the blowout.

The leak had cost the company $763 million through the end of September, according to a financial report. Much of that was expected to be recovered from insurance. The company still faces possible, local, state and federal penalties and fines. It also is fighting more than 200 lawsuits.